One! More! Time!
IP and Bandwidth

9/26/2011 12:01 AM Eastern

JUST UNDER TWO DECADES AGO, AT A NATIONALShow breakfast for engineering mucketymucksin L.A., MIT Media Lab founderNicholas Negroponte, who at the timehad just published Being Digital, causeda few dozen forkfuls of scrambled eggsto quiver with indignation.

Back then, it was a relatively newbit of network blasphemy; today, it’s aperennially popular theme: Bandwidthshould be free!

Fast-forward to now. The work of today’s network engineersis the race to service the dozens of electronicdoodads in our lives, parched for broadband. For them,bandwidth is anything but free, especially if you’re theone girding for the growth in moving all the bits.

Going from A-to-D was one thing, and a big thing.And it’s still in motion.

Just as analog spectrum bows to digital, digitalmorphs. Once, “digital” was the thing that made it possibleto do lots more TV — remember John Malone’s“500 channels”?

The volume of things that become quaint every twomonths is simultaneously exciting and depressing.

So, back to bandwidth basics this week. The bandwidthof IP. A typical cable system is built to 860 Megahertzof total available bandwidth. Some go higher (1Gigahertz); lots go lower (750 MHz). But let’s go in themiddle.

Subtract the upstream path, which representsabout 5% of total available capacity between 5 MHzand 54 MHz. That includes guard band, so that stuffgoing down doesn’t mess with stuff going up.

That leaves 811 MHz, or, about 135 “channels” —where “channel” means a 6 MHz chunk of spectrum.(Will the 6 MHz designation become vestigial? It appearsso. But that’s not for this column.)

Suddenly, the signal path carved out for IP traffic— used by cable modems and voice-over-IP — needsto grow. For more than a decade, two 6-MHz channelscarried everything an operator needed to service highspeedInternet and voice services. Not so now.

By next year, that pool of IP-capable channels couldgo to 12. Why: Because soon enough, the averageU.S. household will contain an average of six screensthat play video from an IP-based signal. That’s roughlytwo times the number of TV screens accustomed to receivingsignal through a set-top box connected to a TV.

Meanwhile, the trend of making everything smallerand lighter — a function of silicon — thrives. Hardwarecedes to software. Lines of code are the new black.(Sigh.)

On the drawing boards or production schedules,depending on who you ask, are chip designs that makeit possible to go “all-IP” — meaning that the entiredownstream spectrum, from 54 MHz to 860 MHz, canbe undone as 6-MHz channels, and treated as a giantpool of IP spectrum.

That’s all a function of bonded DOCSIS 3.0 channels.Bond them all, the logic goes. Use gateways (seelast week’s column) for the transition. In conventionallogic, this transition will take a decade.